Railway cars with one or more hoppers have been used for many years to transport and sometimes store dry, bulk commodities and materials. Hopper cars are frequently used to transport coal, sand, metal ores, ballast, aggregates, grain and any other type of lading which may be satisfactorily discharged through respective openings formed in one or more hoppers. Respective discharge openings are often provided at or near the bottom of each hopper to rapidly discharge cargo. A variety of door assemblies and gate assemblies along with various operating mechanisms have been used to open and close discharge openings associated with railway cars.
Hopper cars may be classified as open or closed. Hopper cars may have relatively short sidewalls and end walls or relatively tall or high sidewalls and end walls. The sidewalls and end walls of many hopper cars are typically reinforced with a plurality of vertical side stakes. The sidewalls and end walls are typically formed from steel or aluminum sheets. Some hopper cars include interior frame structures or braces to provide additional support for the sidewalls. Hopper cars may be generally described as top loading and bottom unloading. Such hopper cars typically require closing gates or doors located underneath the hopper car prior to loading and opening the gates or doors only when the hopper car is at a specific location in an unloading facility. Through use of linkages and one or more power sources such as an air cylinder, a hydraulic cylinder, an electrical motor, capstan drive system or other types of operating mechanisms associated with hopper cars the gates or doors may be closed prior to loading and opened to discharge lading.
A wide variety of techniques and methods have been used for loading and unloading bulk materials from railway cars. For example, bottom dumping hopper cars are often equipped with discharge doors or gates that may be opened as each railway car moves over a pit or an elevated trestle. Various techniques may be used to open discharge doors or gates while the railway car continues to move. Such facilities often include a feeder and a conveyor to move coal or other bulk materials after dumping.
Another technique involves use of a rotary power dumper. Such facilities are frequently used for unloading coal at coal fired electrical power plants.
Side dumping cars have also been used for many years. Side dumping cars typically require an elevated track on a built-up embankment so that the dumped lading will flow over the side of the embankment and not flow back over the tracks on which the cars are moving.
Coal is often shipped in unit trains pulled by several high horse power locomotives. These trains may include over one hundred cars with each car carrying about 100-115 tons of coal. Rotary dump coal cars are often used with such unit trains. Rotary dump coal cars are generally equipped with swiveling or rotary couplers. An unloading facility used with such coal cars generally includes a rotary dumper and an indexing system to properly position each car in the rotary dumper. The rotary dumper may respectively engage each car and a special section of track and rotate both the car and the section of track as a single unit relative to a longitudinal axis extending through rotary couplers of adjacent cars. A rotary power dumper or rotary car dumper typically engages a loaded car, rotates the car through three hundred sixty degrees (360°) and returns the empty car and associated section of track to the original starting position without uncoupling from adjacent cars. Rotary dump unloading facilities are expensive to build and expensive to maintain.
Large quantities of coal and other types of bulk lading are often shipped in open top, bottom dump hopper cars. Because these cars are emptied by dumping from the bottom, unloading equipment and facilities are often located beneath associated tracks to receive the dumped coal or other bulk lading. Sometimes, these facilities include large, rail-supporting I beams suspended over permanent steel hoppers mounted in thick, high strength concrete foundations located beneath elevated railroad tracks. Unloading techniques may include dumping coal in large, relatively long piles under the elevated tracks.
Even though large quantities of bulk commodities may be transported at low costs from one terminal to another, each unloading facility must also maintain favorable economics of railcar transportation for purchases of bulk commodities. If unloading is slow, each train may be delayed for a substantial period of time adding cost per ton for the associated bulk commodities.